How
has the intensity of UVB radiation changed recently in the
Arctic, and what significance might these changes have?

UV
radiation: the unexplored threat to the Arctic

Betsy WeatherheadUniversity of Colorado CIRES / NOAA

The Arctic has
long been an area at high risk from UV radiation damage.
Although the sun never rises far above the horizon, the
highly reflective snow surface results in damaging levels
of UV to unprotected eyes and vertical surfaces such as
faces, trees and shrubs. Normally, ozone in the stratosphere
shields the Earth from much of the harmful UV radiation.
However, recent measurements in the Arctic show long-term
decreases in the amount of ozone overhead, called total
column ozone. In addition, scientists have observed more
frequent episodes of extremely low ozone, particularly during
the springtime.The Arctic contains fragile ecosystems and
peoples facing increasing health challenges. In such an
environment, increased UV radiation may cause more damage
than elsewhere.

Recent changes
in Arctic ozone and UVIn the last few decades, and particularly in the 1990s,
anthropogenic influences on the natural ozone layer have
resulted in severe ozone depletion in polar regions. Ozone
depletion has been considerably larger in the Arctic than
at mid-latitudes: Antarctica and the surrounding areas are
the only regions with more severe ozone depletion. During
springtime in the Arctic, the combined effect of higher
surface reflectivity, rising sun angles and enhanced stratospheric
ozone depletion can result in higher UV levels than have
occurred in the Arctic in recent history. Spring is often
the time when biological systems are most susceptible to
UV damage: natural protective measures, such as pigmentation
and thickening of leaves, have not had time to develop and
fish larvae are most exposed. The combination of biological
sensitivity, already high UV levels and increased ozone
depletion in the spring are likely to result in a more severe
risk to the Arctic environment.

Arctic sensitivity
to UVThe
high UV levels in the Arctic have been known to cause sunburn
(erythema) and snow blindness (photokeratitis) under normal
conditions. UV can affect immune suppression in humans and
cause long-term health problems including cataracts, skin
cancer and a number of related skin diseases. UV effects
on ecosystems are widespread, affecting individual species-particularly
at the base of the food chain-as well as the relative abundance
of species. Certain phytoplankton, for instance, are especially
sensitive to UV, and reductions in their populations impact
not only the individual species, but also organisms that
compete with or feed on these populations. Cod, herring,
pollock, salmonids, and other fish species spawn in shallow
waters where the larvae can be fully exposed to ambient
solar and UV radiation. Higher UV levels can be particularly
damaging to these larvae, and a reduction in the number
of larvae reaching maturity can mean dramatic impacts for
the fishing industry.

UV and multiple
stressorsMultiple stressors
in the Arctic, including pollutants, climate change and
water accessibility may combine non-linearly with the stress
from increased UV radiation. Many of these stressors are
expected to remain significant or, as is the case for climate
change, increase in the Arctic in the coming years. The
few studies that have examined the multiple impacts indicate
that the combined effects may be much more severe than the
individual impacts. Recent research has explored the role
of UV radiation in enhancing the toxicity of certain chemical
compounds, particularly those associated with oil spills
or petroleum contamination. Called photoenhanced toxicity,
the combination of UV light and certain molecules can seriously
injure, and even kill, sensitive species. Results show,
for instance, that 100% of shellfish embryos that were exposed
to three-day-old spill water under UV light were killed.
By contrast, only 40% of the embryos exposed to the same
water under fluorescent (low UV output) light suffered fatalities.

Expectations
for the futureElevated UV
levels due to ozone depletion are expected to continue in
the Arctic. Current estimates indicate that stratospheric
ozone levels will continue to deplete for the next two decades.
Because decreased ozone levels in the Arctic are determined
not only by man-made chemicals, but also by climate change,
it is unclear whether or not, under current international
legislation, Arctic ozone levels will return to normal.